Because climate change and all seasons are too warm.
And because safe the polar bears.
[spoiler]And because I hate summer.[/spoiler]
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You do know that summer isn't based on our distance from the sun right? It's because the northern hemisphere tilts towards the sun, making it warmer. I think, if I remember correctly, that the Earth is actually closer to the sun during our winter but we get less energy from it because of the tilt of the axis.